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Physiology for Meatheads

Training a client correctly requires an understanding of how the human body responds to exercise, or more appropriately, training. The distinction between exercise and training is made very simply, that is exercise has no specific goal and training does. This section of the book is meant to serve as an additional resource and not a supplement to your certification’s teachings on this topic. In this portion of the handbook we will discuss how exercise affects the musculoskeletal system (skeletal muscle, bones, ligaments, tendons, etc.), the cardiopulmonary system, and the nervous system.

Physiology Overview

At the center of all discussions about training and its effect on the human body is physiology, specifically the body’s response to a stressor. You see, the human body has many different processes that occur at various levels of organization, from cells to tissues, and tissues to organ systems, we all possess the ability to maintain homeostasis, or even-keel of our bodies. A stressor is something that has the ability to disrupt homeostasis, and thus cause our body to adapt and acclimate to be better suited to handle the stress. This is the lynchpin of legitimate training, as a failure to disrupt homeostasis does not produce positive adaptations in strength, power, muscle, conditioning, etc. Similarly, too much disruption of homeostasis also precludes successful adaptations, as the stimulus is too great to acclimate to. In the most severe cases, injury or serious bodily harm can result from too much, too soon.

As early as the 1930’s, the Austria-born physician and researcher Hans Selye began talking about stress and various organisms’ response to it. When he coupled Claude Bernard and Walter Cannon’s theories, interior milieu and homeostasis, respectively, he coined the term general adaptation syndrome (GAS). Bernard was a pioneer who realized that the human body (as well as other organisms) had an interior milieu that needed to be maintained irrespective of the external environment. This work was done back in the mid 1800’s and the crux of Bernard’s research can be summed up in the following translation from his French writings:

“The constancy of the internal

environment is the condition for

a free and independent life.”

What this means is that in order to be a freely living being, like humans are, the internal environment of that particular organism must be maintained. How right was Bernard? Well consider this, everything from our body’s temperature, blood sugar, blood oxygen/carbon dioxide, acidity (or basicity), water volume, sodium concentration, potassium levels, etc. are all maintained by the various processes I alluded to earlier. This is where Walter Cannon comes in. Cannon, a Wisconsin born physician, came up with the concept of homeostasis in the 1930’s. Building upon Bernard’s work, Cannon proposed the following four features of homeostasis:

A body must have mechanisms to maintain a steady state

Steady-state conditions require that any tendency towards change must be resisted with factors to prevent this change

The regulating system that determines the steady state must consist of numerous cooperating mechanisms acting simultaneously or successively

Homeostasis is the result of organized self-government, not chance

And so, standing on the shoulders of giants (Cannon and Bernard), Selye took it one step further. He determined that any stressor or stimulus that disrupted homeostasis would cause the body to respond to it in a systematic way, depending on the magnitude of the stress or stimulation. He further categorized these responses into three stages, thus we have come to know Selye’s 3 stages of the General Adaptation Syndrome. The 3 stages can be summarized as follows:

Stage 1-Alarm Phase

A stressor disturbs homeostasis. The brain subconsciously recognizes the stress and activates the fight or flight system (sympathetic nervous system). This part of the nervous system, The Autonomic Nervous System (ANS), is part of the central nervous system (CNS) that regulates bodily functions that are not consciously controlled (blood pressure, gut motility, digestion, etc.). The hypothalamus, the control center of the brain for these autonomic functions, determines the overall reaction to the stressor, i.e. if extra energy is required to deal with the stressor adrenaline/norepinephrine is released to increase heart rate, increase blood pressure, increase sugar liberated from the liver, dilates the pupils, etc.

Think about lifting a heavy weight. It would be almost impossible to do this in a resting state, but rather when you decide you’re going to go and lift the weight (or someone commands you to do so) you start preparing your body to do the task, subconsciously. Your hear rate and blood pressure increases, the blood flow to your skeletal muscles increases (and blood to the gut decreases), pupils dilate, etc. This is activation of the alarm system, or Stage 1 of the GAS.

Stage 2-Resistance Phase

After the alarm phase, the body begins to react to the stressor to allow the body to return to equilibrium, or homeostasis. We classically refer to this as recovery in exercise science, but it also has much broader applications to other physiologically regulated phenomena.

After a serious bout of training there ought to be a period of time for recovery. If this does not occur, the alarm phase is more prolonged and is of greater magnitude. If this happens chronically over long periods of time, there is a high potential for someone to enter into the third phase of the GAS, the exhaustion phase.

Stage 3- Exhaustion Phase

In the exhaustion phase of the GAS, both the physical and psychological energy available to fight a stressor are seriously depleted. This does not usually occur in acute situations, although serious cases of doing way too much, too soon can cause people to enter this phase from exercise.

The most common example of this is when an former athlete or high level trainee returns to exercise after a long layoff and tries to do the same things he or she was doing before. Unfortunately, the body is not ready to deal with this much stress at this time and serious complications like rhabdomyolysis, which is characterized by a physical breakdown of the muscle tissue and subsequent releasing of its contents in the blood stream causing kidney and other organ problems, thus resulting in “Coca-Cola like urine” due to the myoglobin (oxygen carrying protein in muscles) in the urine. This can be life threatening if not treated.

So if Selye, Cannon, and Bernard wanted us to know anything, it’s that we possess the machinery to adapt to stress, but the level of stress needs to be appropriate to our current level of adaptation. This is paramount in the training world, as too little or too great of stress will cause distress– the wrong amount of stress. Distress results in no adaptation of the trainee, either because the stress isn’t great enough to initiate the Alarm phase or because it’s too much and the trainee skips right to the Exhaustion phase. When given just the right amount of stress,also known as eustress, the trainee enters the alarm phase and subsequently the resistance phase, thus successfully adapting to the training. In short, the poison is in the dose. Given the correct dose of exercise and the trainee will get better, stronger, faster, leaner, etc. Given too much or too little of the medicine (exercise), and the lifter either goes nowhere or gets worse.

*look for the finished e-book sometime around Christmas!
-thefitcoach

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About thefitcoach

An aspiring physician, I've been involved in the strength and conditioning world for over 5 years now in a professional sense. I started this blog with some like-minded individuals to share our thoughts on training, nutrition, lifestyle, medicine, health, and everything in between.